1. Field of the Invention
The present invention relates to a local area network (LAN) and a communication network. More specifically, the invention relates to a method for controlling communication in a mobile Integrated Voice and Data (IVD) system, the system having a plurality of Cell Stations (CSs) interconnected through communication networks, including a LAN and a PBX telephone network, and Personal Stations (PSs) movable among a plurality of radio cells, each CS having a particular radio cell which defines a territory in which a PS is capable of communicating with the CS via a radio link. In particular, the invention relates to a method for controlling communication of the mobile IVD system having a plurality of PSs, wherein the method enables the sending of calls to PSs and also enabling automatic re-connection of a link even when the PS moves between radio cells during telephone calls and the link is disconnected.
2. Background of the Invention
A well-known PBX system comprises a plurality of PBX telephones interconnected with specifically used communication wires the inside of buildings, schools, and enterprises (or offices in enterprises). In addition, a recent development of radio technology has been promoting the development of mobile IVD systems in which the PBX telephone service is based on a physically separated form of CSs and PSs that can communicate via radio. The system allows users (subscribers) to actually exchange information with each other using PSs while the CS controls the communication link among the PSs.
The territory in which CSs are capable of communicating with PSs is restricted to a predetermined area due to the attenuation of radio waves as a result of the surrounding environment (a territory in which a CS is capable of communicating is generally called a radio cell). Each CS accommodates or services within its own radio cell one or more PSs. PBX telephone numbers of private links are assigned to each of the PSs which allow communication between the PSs.
On the other hand, PSs are not mechanically constrained and may move freely between a plurality of radio cells in accordance with the needs of the users. In addition, when mobile IVD systems are not capable of sending and receiving some information to or from PSs via CSs, the significance of the mobile IVD system will be decreased.
However, a conventional mobile IVD system must be substituted with a PBX having the following additional functions so that the system has a new link which enables constant reception of information with respect to PSs moving among a plurality of radio cells:
(a) a function for sending call signals to mobile terminals from all the CSs; and PA1 (b) a function for selecting the optimal CS to connect a link by a response from the PS to the call signals. PA1 (c) a function for monitoring the receiving level of electromagnetic waves from PSs and selecting the optimal CSs; and PA1 (d) a function for disconnecting the communication circuit whose receiving level has weakened in synchronization with the PSs. PA1 The quality of cordless telephone system shall be able to be secured to a level more than equal to the counterpart conventional analog type cordless telephone system, the secrecy of conversation on the phone can be improved and the frequency bandwidth can be effectively used. PA1 PSs shall be capable of basic connection with CSs at various places such as offices, homes, and outdoor areas. PA1 In addition, when there arises a situation in which PSs already used for homes and offices must be connected to outdoor public CSs, the PS can be easily shared through the execution of necessary measures. PA1 The second generation cordless telephone system shall be able to be connected with the established analog telephone network and ISDN digital network. PA1 (d) In addition to service that has been used in conventional cordless telephone systems, various services can be utilized through the services provided by ISDN. PA1 (a) in response to a first PS moving into a territory of a first CS, registering the LAN identifier of the first PS and assigning a PBX number to the first PS by the first CS; PA1 (b) sending calling information including the LAN identifier of the second PS and the first PSs newly assigned PBX telephone number to said first CS via radio links by the first PS; PA1 (c) broadcasting the calling information from the first CS to all the other CSs via the LAN by the first CS; PA1 (d) in response to a second CS which registers the second PS receiving the calling information, resending it to the second PS via radio links by the second CS; PA1 (e) dialing the PBX telephone number stored in the calling information by the second PS; and PA1 (f) calling the first PS via a PBX link in response to dialing step (e) and establishing a PBX telephone link between the first and second PSs. PA1 (a) establishing the communication link between a first PS within a radio cell of a first CS and a second PS within a radio cell of a second CS; PA1 (b) instantly disconnecting the communication link if the first PS moves beyond the radio cell of the first CS and the reception level of radio waves received by the first CS from the first PS falls to or below the predetermined threshold value; PA1 (c) registering the LAN identifier of the first PS in a third CS, and simultaneously assigning a PBX telephone number to the first PS when the first PS moves to the radio cell of the third CS; PA1 (d) sending by the first PS of moving information having the LAN identifier of the second PS and the newly assigned PBX telephone number through radio links to the third CS; PA1 (e) sending by the third CS of the sent moving information via the LAN to the second CS; PA1 (f) sending by the second CS of the sent moving information by radio signal to the second PS; PA1 (g) dialing by the second PS of the PBX telephone number identified in the sent moving information; and PA1 (h) calling the first PS in response to the dialing step, and then re-establishing the PBX telephone link between the first PS and the second PS in response to the calling.
In addition, conventional mobile IVD systems require substitution to a PBX having the following additional functions to automatically switch over the communication circuit in order that the continuation of conversation be guaranteed to PSs moving between radio cells during communication.
However, substituting a PBX equipped with the above construction (a) to (d) for all the PBX telephone links in the mobile IVD system imposes a considerable cost burden as far as the users of the system are concerned. Furthermore, conventional PBX systems prevent users from enjoying the benefit of radio communication.
In this regard, the concept of the second generation cordless telephone, which is referred to as a digital cordless telephone, or PHP (personal handy phone) has recently been formulated. PHPs allow the simultaneous handling of communication by means of both voice and data signals through the digitization of voice and data signals. Technological specifications for the interface between general-purpose radio segments has been standardized on the part of RCR (R & D Center for Radio Systems) between the PHP terminal and CS. PHP can simultaneously handle both voice and data with the digitization thereof via the interface between radio segments.
The second generation cordless telephone system satisfies the following items as basic functions:
(a) Digitization of system
(b) Interconnection
(c) Connection with communication network